Many hundreds of strains of Bacillus thuringiensis (B.t.) produce insecticidal toxins designated as delta endotoxins. They are synthesized by sporulating B.t. cells. When toxin is ingested by a susceptible insect, the cells of the gut epithelium are destroyed.
The reported activity spectrum of B.t. covers insect species within the orders Lepidoptera and Coleoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitoes and black flies. See Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C. (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Dipteran insects are serious nuisances as well as being vectors of many serious human and animal diseases such as malaria, onchocerciasis, equine encephalitis, and dog heartworm.
The two varieties of B.t. known to kill mosquitos and blackflies are B.t. israelensis (B.t.i.) (Goldberg, L. J., J. Margalit [1977] Mosquito News 37:355-358) and B.t. morrisoni (B.t.m.) (Padua, L. E., M. Ohba, K. Aizawa [1984] J. Invertebrate Pathology 44:12-17). These are not harmful to non-target organisms (Mulla, M. S., B. A. Federici, H. A. Darwazeh [1982] Environmental Entomology 11:788-795), and play an important role in the integrated management of dipteran pests. They are safe to use in urban areas, and can be used in aquatic environments without harm to other species.
Dipteran pests are a major problem in the poultry and cattle industries. The horn fly, a serious cattle pest, is killed by B.t. in the larval stages (Temeyer, K. B. [1990] "Potential of Bacillus thuringiensis for fly control," Fifth International Colloquium on Invertebrate Pathology and Microbial Control, Society for Invertebrate Pathology, 352-356).
There are also dipteran pests of plants, such as Hessian fly, Medfly, and Mexfly, for which a B.t. product would be very valuable.